The objective of the proposed research is to determine the effect of route of administration on the efficacy of cyclophosphamide in cancer patients, as judged by pharmacokinetics of its biologically-active metabolites. Determination of the areas-under-the-blood-decay-curve (AUC) for cyclophosphamide, 4-hydroxycyclophosphamide (the primary metabolite of cyclophosphamide on the activation pathway), and phosphoramide mustard (the ultimate cytotoxic metabolite of cyclophosphamide) in 18 cancer patients after intravenous or oral administration is proposed. Each patient will serve as his own control by receiving cyclophosphamide intravenously and then orally 30 days after intravenous administration. Blood samples will be collected at various times from 5 minutes to 24 hours after drug treatment, and 4-hydroxycylophosphamide will be stabilized by immediate reaction with cyanide to form aldophosphamide cyanohydrin. Phosphoramide mustard will be stabilized as its methyl ester by reaction of blood extracts with diazomethane. For quantitation of metabolites, tracer amounts of radiolabeled cyclophosphamide will be added to the clinical drug preparation for intravenous or oral administration. Metabolites and uncharged drug will be isolated from blood samples by chloroform extraction (for 4-hydroxycyclophosphamide and cyclophosphamide) or by methanol extraction (for phosphoramide mustard). Metabolite isolation and identification will be accomplished by thin-layer co-chromatography with synthetic standards combined with detection by 4-(p-nitrobenzyl)pyridine. Quantitation will be accomplished by radioassay of chromatographically-isolated metabolites. Relative AUC values for 4-hydroxycyclophosphamide and phosphoramide mustard resulting from intravenous or oral administration will be compared as an indication of the more efficacious route of drug treatment.